By David Russell, reporter at OptionMonsterNEW YORK -- The bulls are back in Stryker ( SYK). Late last year, traders snapped up the January 48 calls, which more than doubled in value as the maker of replacement hips and knees pushed higher. Wednesday activity shifted to the April 55 calls, which traded in large blocks for 65 cents shortly after the open, according to OptionMonster's real-time systems. Volume approached 2,800 contracts, almost triple the previous positioning. Those calls lock in the price investors must pay for the shares. Their relatively cheap price gives them big leverage to even modest gains in the stock on a percentage basis. However, they have a limited lifespan and will expire worthless if the stock fails to move. Stryker continued higher throughout the session and closed at $54.23 Wednesday, up 1.69%. Those same calls would fetch 90 cents and 95 cents by the afternoon, a gain of about 40%. The company is scheduled to report earnings after the bell on April 17. Overall options volume was triple the daily average Wednesday, with calls outnumbering puts by 19 to 1. Russell has no positions in SYK.